The invention relates generally to a method and apparatus for determining forces to be applied to a user interacting with virtual objects in a virtual reality computer environment and more specifically to a method and apparatus for determining forces to be applied to a user through a haptic interface.
Virtual reality (VR) computer systems generate simulated environments called xe2x80x9cvirtual environmentsxe2x80x9d for interaction with a user. The virtual environments include virtual representations of objects which the user can manipulate through an input device. Conventional VR systems attempt to simulate the visual, audio and touch sensory information which would be accessible to a user in the real world environment when interacting with physical objects. These VR systems also attempt to give the user the control over objects that the user would have in the real world environment.
VR system applications include video games, engineering tools and training tools. VR systems have been used to replicate situations which would be too costly or too dangerous to create otherwise. One example of a VR system which is used as a training tool is a flight simulator. Flight simulators replicate cockpits of airplanes and are used to train pilots without subjecting the pilots to the danger of actual flight.
The more sophisticated VR systems include a haptic interface system. A haptic interface system allows a human xe2x80x9cobserverxe2x80x9d to explore and interact with a virtual environment using the sense of touch. The major goal of a haptic interface system is to provide the sensations a user would experience if the user were to touch a virtual environment. Haptic interface systems replicate the forces felt by humans when interacting with real objects.
The two different forms of human haptic perception that haptic interface systems attempt to replicate are tactile and kinesthetic. The human tactile system consists of nerve endings in the skin which respond to pressure, warmth, cold, pain, vibration and itch. The tactile system allows humans to sense local geometry, rough texture, and thermal properties from static contact. The kinesthetic system refers to the collection of receptors in the muscles, tendons, and joints which allow perception of the motion and forces upon a human""s limbs. In order to accurately replicate the forces experienced by humans in the real world, haptic interface systems attempt to model the shape, surface compliance and texture of objects.
Haptic interface systems include three main components: a haptic interface device, a model of the environment to be touched, and a haptic rendering application. A haptic interface device is a tactile or force-feedback device used by a human which provides the touch sensations of interacting with virtual objects. Known haptic interface devices consist of an electro-mechanical linkage which can exert a controllable force on a human""s hand. The model of the environment is a computer generated representation of the real world environment. The haptic rendering application determines the forces to be applied to the user based on the model environment.
One known haptic interface system reduces the user""s interactions with the virtual environment to those of a point interacting with three dimensional objects. The haptic rendering application used in this known system utilizes vector field methods to determine the force to be applied to the user. Vector field methods are a classification for any method that can determine the feedback force to be applied to a user by knowing only the location of the haptic interface point. As used herein, a xe2x80x9chaptic interface pointxe2x80x9d is defined as the endpoint location of the physical haptic interface as sensed by the encoders of the VR system. The haptic interface point represents the location of the user in the virtual environment. Vector field methods however, do not accurately replicate the touch sensations a user would experience for many objects in the real world. Users using a haptic interface system which utilizes a vector field method may experience force discontinuities when traversing the volume boundaries of the virtual objects.
Further, vector field methods also do not accurately model thin objects. Due to the limited servo and mechanical stiffnesses, the haptic interface point must travel somewhat into the object before enough force can be applied to the user to make the object feel xe2x80x9csolid.xe2x80x9d When this distance becomes greater than the thickness of an object, the vector field method produces unrealistic sensations. For example, when the haptic interface point penetrates more than halfway through a thin object, rather than exerting a force to push back against the user, the force vector changes direction and applies a force which pushes the user out the side of the object opposite to the side that the user entered. Vector field methods also cannot determine the appropriate forces to apply when the model of the environment overlaps simple objects to create more complex objects.
What is desired then is a haptic interface system which provides touch interfaces which accurately replicate the touch sensations a user would experience in the real world. The present invention permits such functionality.
The invention relates to a method for determining the forces to be applied to a user through a haptic interface. The method includes the steps of generating a representation of an object in graphic space, sensing the position of a user in real space, determining the user""s haptic interface in graphic space, determining the user""s fiducial object in graphic space and determining a force to be applied to the user in real space. In one embodiment the method calculates a stiffness force to be applied to the user. In other embodiments, the method calculates damping and friction forces to be applied to the user.
In one embodiment, the step of generating a representation of an object in graphic space includes defining the object as a mesh of planar surfaces and associating surface condition values to each of the nodes defining the planar surfaces. In another embodiment, the step of generating a representation of an object in graphic space includes describing the surface of the object using a coordinate system and associating surface condition values with each set of coordinates.
The invention also relates to an apparatus for determining the forces to be applied to a user through a haptic interface. The apparatus includes a position sensor, a processor executing an algorithm to determine the forces to be applied to a user in real space, a display processor and a force actuator. In one embodiment, the algorithm determining the forces to be applied to the user includes a module generating a representation of an object in graphic space, a module determining the user""s haptic interface in graphic space, a module determining the user""s fiducial object in graphic space and a module calculating the force to be applied to the user in real space.
The present invention has the technical advantage of accurately replicating the touch sensations a user would experience when interacting with real world objects. The present invention has the further advantage of accurately modeling the forces applied to a user by thin and arbitrarily shaped polyhedral objects. The present invention has yet the further advantage of determining the appropriate forces to be applied to a user by a complex virtual object formed from overlapped simple virtual objects.